1. Field of the Invention
The present invention is related generally to optical sources, and in particular to a high radiance incoherent light source for coupling to an optical fiber.
2. Background of the Invention
In biomedical applications, as well as other applications requiring stimulation of fluorescence or other similar illumination requirements, a broadband optical source is typically needed, as the speckle field generated by narrowband illumination makes narrowband illumination unsuitable for many biomedical and imaging applications, such as optogenetics applications. Historical broadband incoherent light sources require relatively large optical systems and reflectors to concentrate light in a narrow beam in order to provide an efficient source of illumination, and to provide high intensity when coupling into a waveguide such as an optical fiber.
Existing broadband solid state sources such as broadband light-emitting diodes (LEDs) such as those used for general illumination are attractive for providing efficient and compact broadband illumination sources. Semiconductor lasers are often used as narrowband optical sources and produce narrow beams suitable for coupling to an optical waveguide. However, present-day broadband (“white”) LEDs are in fact LED-stimulated fluorescent crystals that do not produce narrow beams and have relatively low radiance, making them generally unsuitable for introducing high-radiance illumination to an optical fiber. The LEDs used to stimulate the crystals are typically blue LEDs that stimulate a Ce:YAG crystal located within a diffusing broadband cavity.
Therefore, it would be desirable to provide an optical source having the advantages of solid state sources, while providing a compact high-radiance source of broadband light that can be coupled to an optical fiber.